JP6897532B2 - Electrolytic solution for extracting metal compound particles, and electrolytic extraction method using it - Google Patents

Description

The present invention relates to an electrolytic solution used when a metal material is etched in an electrolytic solution to extract metal compound particles in the metal material, and an electrolytic extraction method using the electrolytic solution.

Metallic materials, especially steel materials, are required for steel materials by controlling the types of inclusions and precipitation phases present in the material matrix, shapes such as aspect ratios, dimensions, etc. by means of trace addition elements and various heat treatments. Controlling strength and properties is widely practiced.
Therefore, observing inclusions and / or precipitated phases and measuring their components and quantities are important for quality control of steel materials and analysis of manufacturing processes.

In order to observe inclusions and precipitated phases by SEM or the like, it is necessary to expose the inclusions and precipitated phases buried in the matrix to the observation surface. Conventionally, electrolysis has been performed in various electrolyte solutions. , The inclusions and the precipitated phase are exposed on the sample surface so that they can be observed.

In recent years, due to advances in steel material manufacturing technology, the types of inclusions and precipitated phases have diversified, and fine dispersion has also progressed. When observing, only the matrix (Fe) is selectively dissolved and inclusions are made. With respect to substances and precipitated phases, even if they are fine particles, an electrolytic solution that is surely retained on the observation surface and does not dissolve is required.

In addition, when identifying and quantitatively analyzing these inclusions and precipitated phases, similarly, the matrix of the steel sample is dissolved in the electrolyte solution, and the inclusions and precipitated phases are recovered as an electrolytic residue and identified. Quantitative analysis is being performed.

In the case of this quantitative analysis, only the matrix portion of the steel material is efficiently electrolyzed, the Fe content is reliably dissolved and retained in the electrolytic solution, and other inclusions and the portion corresponding to the precipitated phase are electrolyzed. It is required that it can be reliably recovered as a residue.

Non-Patent Document 1 examines the problem that when CaO is the main component and is chemically unstable, such as slag-based inclusions and powder-based inclusions, it dissolves in the extraction process and cannot be evaluated. It is stated that powder-based inclusions are difficult to dissolve and can be extracted quantitatively in the case of constant current electrolysis using the electrolytic solution of.

Patent Document 1 relates to a method for extracting Ca (calcium) -based inclusions in steel and a method for segregating and quantifying, and examines the problem that it is difficult to extract CaO and accurately segregate and quantify CaO. In the decomposition / extraction process, CaO reacts with the moisture in the atmosphere and changes to another form, which is considered to be because it is easily dissolved in the solvent, and the operation from the decomposition of the steel matrix to the collection of the residue is performed in a dry atmosphere (glove). It is proposed to do it in the box).

Japanese Unexamined Patent Publication No. 06-174716

Atsushi Chino et al., Development of extraction, separation and quantification method of Ca-rich oxides in steel by constant current electrolysis, iron and steel vol. 93 (2007) No. 2, p105-110

Precipitates and inclusions that are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol may dissolve in the electrolytic solution, making electrolytic extraction difficult. MgS can be mentioned as an example of such precipitates and inclusions. MgS is a finely dispersed particle having a high γ grain pinning ability, and is said to be useful for improving toughness and the like. However, since MgS is easily decomposed even by etching with an electrolytic solution, accurate data on the size distribution and the number density of MgS cannot be obtained, which is a big limitation in material development. As described above, there is a demand for an electrolytic extraction method for obtaining accurate data on easily soluble precipitates and inclusions.

The inventors of the present application have been working on improving the measurement accuracy of steel material analysis, and in the previous research, inclusions were found in the analysis of metal compounds in steel materials due to electrolytic corrosion in non-aqueous solvent-based electrolytic solutions. In the fine particles of the precipitation phase, especially various metal compounds, especially the surface layer of MnS, a phenomenon of unknown cause is observed in which CuS having a concentration higher than the content measured by means other than the electrolytic operation is observed. Therefore, it has been found that MnS particles may be detected as if they were CuS (Artifact CuS).

As a result of investigating the cause of the artificial imitation (Artifact) in detail, the inventors of the present application generated a metal ion (Cu ²⁺ _{) having a small solubility product K sp in} the electrolytic solution by the electrolytic operation, and as a result, a metal sulfide (MnS) ), It was discovered that a metal ion (Mn ^{2+ ) having a large solubility product Ksp is replaced with a metal ion (Cu 2+} ) having a small solubility product Ksp. It was also found that such substitution of metal ions on the surface of sulfide easily proceeds at normal temperature and pressure and even in an aqueous solution or a non-aqueous solvent.

As a result, inclusions and precipitated phases that originally existed as MnS in the steel sample will be observed as CuS as long as the surface is observed, and Cu ions in the electrolytic solution will be observed on the surface of MnS. By exchanging CuS due to the above with MnS having a thickness of about several tens of nm (1 to 100 nm), even if mass spectrometry is performed from the residue, in the case of fine particles, CuS occupies a considerable part of the volume. Therefore, accurate quantification was impossible.

In the previous research by the inventors of the present application, as a method for suppressing the above-mentioned fictitious (artifact), a metal (attack metal) forming an artifact (fictitious) metal sulfide in a solvent-based electrolytic solution was selectively selected. It was conceived that by adding a trapping agent (chelating agent, etc.), the free attack metal in the electrolytic solution was reduced and Artifact (fictitious) metal sulfide was not produced.

However, in the case of precipitates and inclusions such as MgS, which are more easily hydrolyzed than MnS, they are dissolved in the electrolytic solution, so that electrolytic extraction has been considered impossible in the past. As a matter of course, even if a drug (chelate or the like) that supplements the attack metal that causes fiction (Artifact) is added, it is not possible to suppress the dissolution of easily soluble precipitates and inclusions.

As a result of diligent studies on this problem, the inventors of the present application have conceived that a waterproof barrier sheet such as Ag or AgS can be formed on the surface of precipitates such as MgS and inclusions that are easily dissolved by using an ion exchange reaction. .. That is, precipitates and inclusions such as MgS have a large solubility product Ksp and are easily dissolved, but by including a compound having a small solubility product Ksp (for example, AgS or Ag) in the electrolytic solution, the solubility product Ksp is large. It was expected that the surface of the (easily soluble) precipitates and inclusions would be coated with a compound having a small solubility product Ksp (difficult to dissolve) or the like, and would be difficult to dissolve. Actually, the inventors of the present application attached a mirror-polished MgS-containing steel material to an electrolytic solution to which Ag was added, and conducted an electrolytic extraction experiment. As a result, an ion exchange reaction between Mg and Ag occurred on the MgS surface layer to make it waterproof. It was confirmed that a sex barrier sheet could be formed.

In the above, (the case where the ion exchange reaction between Mg atom and Ag atom on the MgS surface occurs and a waterproof barrier sheet by Ag is formed on the MgS surface has been described, but the same phenomenon occurs in combinations other than Mg and Ag. can be estimated to be expressed. in other words, replacement of the metal ions at the surface metal compound, solubility magnitude difference corresponds to the product K _sp when there is (10 digits (10 ¹⁰⁾ of about or more magnitude difference) easily progresses More specifically, when the difference in pK _{sp of two compounds having different solubility products K sp} (hereinafter sometimes referred to as Δ) is about 10 or more, the pK _sp is large (solubility product K _sp). It can be estimated that the substitution of the compound having a small _{pK sp} and the compound having a small pK sp (with a large solubility product) proceeds easily.
The above condition can be expressed by the following equation.
Δ = pK _sp [Compound ( _{smaller K sp} )]-pK _sp [Compound ( _{larger K sp} )]
= (-Log ₁₀ K _sp [Compound ( _{small K sp} )])-(-log ₁₀ K _sp [Compound ( _{large K sp} )])
≧ 10
Here, the solubility product K _sp of a certain compound is expressed as K _sp [compound], and pK _sp [compound] = −log ₁₀ K _sp [compound].

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) An electrolytic solution in which a metal material is etched in an electrolytic solution to extract metal compound particles in the metal material.
The solubility product of the _{metal compound M x} A _{y to} be extracted contained in the metal material _{is K sp} [M _x A _y ].
When _'the solubility product _{K sp} [M' metal compound M _'x' A _y and _{x 'A y'],}
An electrolytic solution characterized by containing ions of a metal M'defining by the following formula and having a Δ of 10 or more.

_{Δ = pK sp [M 'x} ' A y '] -pK sp [M x A y]
_{= (- log 10 K sp [} M 'x' A y ']) - (- log 10 K sp [M x A y])

Here, M and M'are different metal elements, A is a single atom or atomic group forming a compound with M or M', and x, x', y, y'are of M, M', A. It represents the composition ratio of the compound determined by the valence, and the solubility product K _sp is a value in an aqueous solution at 25 ° C.

(2) The electrolytic solution according to (1) above, which is a non-aqueous solvent type electrolytic solution.

(3) The electrolytic solution according to (1) or (2) above, wherein the metal compound M _x A _{y to be extracted is MgS.}

(4) The above-mentioned (1) to (3), wherein the metal M'is at least one of Hg, Ag, Cu, Pb, Cd, Co, Zn, and Ni. Electrolyte.

(5) The electrolytic solution according to any one of (1) to (4), wherein the concentration of the metal M'is 0.0002 to 0.2% by mass.

(6) The electrolytic solution according to any one of (1) to (5) above, wherein the metal material is a steel material.

(7) The electrolytic solution according to any one of claims 2 to 5, wherein the non-aqueous solvent contains at least one of methanol and ethanol.

(8) In a method of etching a metal material in an electrolytic solution and electrolytically extracting metal compound particles in the metal material.
Using the electrolytic solution according to any one of (1) to (7), _{the particles of the metal compound M x} A _y to be extracted are extracted in a form in which at least the surface is coated with the metal M'or the compound. , A method for extracting metal compound particles.

-According to the present invention, it is possible to suppress the dissolution of precipitates and inclusions which are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol in an electrolytic solution. As a result, it is possible to provide an electrolytic solution capable of obtaining accurate data on their precipitates, size distribution of inclusions, and number density, and an electrolytic extraction method.

It shows an example of the sketch of the electrolytic apparatus using the electrolytic solution which concerns on this invention. It is a chart which shows the SEM photograph and the element concentration of the fine particle of the steel sample surface etched by using the electrolytic solution which concerns on this invention. It is a schematic cross-sectional view of the fine particles obtained by etching using the electrolytic solution which concerns on this invention.

According to the present invention, an electrolytic solution in which a metal material is etched in an electrolytic solution to extract metal compound particles in the metal material.
The solubility product of the _{metal compound M x} A _{y to} be extracted contained in the metal material _{is K sp} [M _x A _y ].
When _'the solubility product _{K sp} [M' metal compound M _'x' A _y and _{x 'A y'],}
Provided are an electrolytic solution containing ions of a metal M'defining by the following formula and having a Δ of 10 or more, and a method for extracting metal compound particles using this electrolytic solution.

_{Δ = pK sp [M 'x} ' A y '] -pK sp [M x A y]
_{= (- log 10 K sp [} M 'x' A y ']) - (- log 10 K sp [M x A y])
Here, M and M'are different metal elements, A is a single atom or atomic group forming a compound with M or M', and x, x', y, y'are of M, M', A. It represents the composition ratio of the compound determined by the valence, and the solubility product K _sp is a value in an aqueous solution at 25 ° C.

The present invention relates to the extraction of metal compound particles in a metallic material. More specifically, by etching the metal material in the electrolyte solution, the matrix (Fe, etc.) is selectively dissolved, and the metal compound particles such as inclusions and precipitation phase contained in the metal material are exposed on the sample surface. .. As a result, the metal compound particles can be made observable.
Examples of the method for extracting fine particles in the metal sample include an acid decomposition method in which the iron matrix of the steel sample is dissolved in an acid solution, a halogen dissolution method in which the iron matrix of the steel sample is dissolved in an iodine-methanol mixed solution or a bromine-methanol mixed solution. A non-aqueous solvent-based constant current electrolysis method, a non-aqueous solvent-based constant potential electrolysis (SPEED: Selective Potentiostatic Etching by Electrolytic Dissolution Method) method, or the like can be used. Of these, the SPEED method using a non-aqueous solvent is suitable because when the fine particles are dispersed in the solvent, the composition and size are unlikely to change, and even unstable fine particles can be extracted relatively stably. The present embodiment will be described by taking as an example a method for evaluating fine particles in a steel material by a non-aqueous solvent-based constant potential electrolysis method (SPEED method) with reference to FIG. 1, but the extraction method in the present invention is described. The metal material is not limited to the SPEED method, and the metal material is not limited to the steel material.

First, the metal sample 4 is processed to a size of, for example, 20 mm × 40 mm × 2 mm, and an oxide film such as a scale on the surface layer is removed by chemical polishing or mechanical polishing to expose the metal layer. .. On the contrary, when analyzing the fine particles contained in the oxide film layer, the fine particles are left as they are.

Next, this metal sample is electrolyzed using the SPEED method. Specifically, the electrolytic cell 10 is filled with the electrolytic solution 9, the metal sample 4 is immersed therein, and the reference electrode 7 is brought into contact with the metal sample 4. The platinum electrode 6 and the metal sample 4 are connected to the electrolyzer 8. Generally, when the above electrolysis method is used, the electrolysis potential of the fine particles in steel such as precipitates has a higher electrolysis potential than the electrolysis potential of the metal portion that becomes the matrix of the metal sample 4. Therefore, it is possible to selectively dissolve only the matrix by setting the voltage between the electrolytic potentials in which the matrix of the metal sample 4 is dissolved by using the electrolytic device 8 and the fine particles such as precipitates are not dissolved. It becomes. Occlusions or the precipitated phase 5 emerge on the surface of the sample in which Fe in the surface matrix portion is electrolytically eluted, and the state is suitable for observation by SEM or the like. Further, the electrolysis can be continued to separate the inclusions and the precipitated phase from the sample surface, recovered as the electrolytic residue 11 (not shown), filtered and separated from the electrolytic solution, and subjected to identification / quantitative analysis.

The electrolytic solution for the metal material according to the present invention, that is, the Fe matrix on the surface for observing inclusions and precipitated phases is electrolyzed, and the Fe matrix is electrolyzed for quantitative analysis of inclusions and precipitated phases. The electrolytic solution used for electrolysis for recovering the residue is preferably
(1) Complex forming agent for Fe ions,
(2) An electrolyte for ensuring the conductivity of the electrolytic solution,
(3) A solvent for holding the formed complex such as Fe in a liquid,
including.

As the complex-forming agent for Fe ions, one or more of acetylacetone, maleic anhydride, maleic acid, triethanolamine, salicylic acid, and methyl salicylate may be selected.

As the electrolyte, one or more types can be selected from tetramethylammonium chloride (TMAC), sodium chloride (NaCl), and lithium chloride (LiCl).

The solvent needs to be a solvent that can hold various complex-forming agents and complexes of these and Fe in a dissolved state, and may be a non-aqueous solvent. Aqueous electrolytes decompose various precipitates even at relatively low electrolytic voltages (for example, -300 mV or less), whereas non-aqueous solvent electrolytes have a wide stable electrolytic region, and are superalloys, high alloys, and stainless steel. It can be applied to almost all steel materials from to carbon steel. When a non-aqueous solvent-based electrolyte is used, only the dissolution of the matrix and the (complexing) reaction between the dissolved Fe ions and the chelating agent occur, and the inclusions or the precipitated phase 5 are not dissolved. It is possible to perform three-dimensional observation and analysis in an "in situ" state on the base material. As the non-aqueous solvent, a compound that facilitates electrolysis and dissolves an organic compound that can be complexed and a supporting electrolyte is suitable, and for example, a lower alcohol such as methanol, ethanol, or isopropyl alcohol is used. Can be done. Methanol, ethanol, or a mixture thereof can be selected. Further, any solvent having the same or higher polarity (dipole moment, etc.) as these alcohols can be used.

In the conventional constant potential electrolysis method, the electrolytic solution is, for example, 10 mass% acetylacetone (hereinafter referred to as "AA") -1 mass% tetramethylammonium chloride (hereinafter referred to as "TMAC")-methanol solution, or 10 mass%. A maleic anhydride-2% by mass TMAC-methanol solution is used. These electrolytic solutions are often used because the electrolytically eluted Fe forms a complex, which is preferable from the viewpoint of dissolving the formed Fe complex in the electrolytic solution.

However, in the conventional electrolytic solution, precipitates and inclusions such as MgS, which are more easily hydrolyzed than MnS, are dissolved in the electrolytic solution, and it is considered that electrolytic extraction is impossible. As a matter of fact, even if the steel material containing MgS was electrolytically extracted using a conventional electrolytic solution, MgS could not be confirmed in the extract or inclusions.

In general, the ease of dissolving a metal compound in an electrolytic solution can be arranged by the size _{of the solubility product K sp.} That is, the _{larger the solubility product K sp} (in other words, the _{smaller the pK sp} (= -log ₁₀ K _sp )), the easier it is to dissolve. Electrolytic solution of the present invention, in order to suppress the dissolution of the (large solubility product K _sp) metal compounds such easily soluble, sparingly soluble (solubility product K _sp is smaller) in the electrolyte the metal of the metal compound Containing ions. A metal compound that is easily soluble ( _{large solubility product K sp} ) is easily dissolved (solubility product K _sp ) by causing an ion exchange reaction with a metal ion of a metal compound that is difficult to dissolve (small solubility product K sp) in an electrolytic solution. The surface of the metal compound (with a large K _sp ) is coated with a metal compound that is _{difficult to dissolve (the solubility product K sp is small).} That is, a waterproof barrier sheet made of a metal compound that is difficult to dissolve is formed on the surface of the metal compound that is easily dissolved. As a result, the dissolution of the easily soluble metal compound in the electrolytic solution is suppressed, and the easily soluble metal compound can be extracted.

The extraction target, easily soluble in the (solubility product _{K sp} large) metal compound _M x _{A y,} slightly soluble (solubility product _{K sp} less) metal compound M _'x' A _y ', the difference in solubility product When there is a magnitude difference of about 10 digits (10 ¹⁰ ) or more, more specifically, when Δ defined by the following formula is 10 or more, dissolution of a easily soluble metal compound in an electrolytic solution is suppressed. Therefore, it becomes possible to extract the easily soluble metal compound.

_{Δ = pK sp [M 'x} ' A y '] -pK sp [M x A y]
_{= (- log 10 K sp [} M 'x' A y ']) - (- log 10 K sp [M x A y])
Here, M and M'are different metal elements, A is a single atom or atomic group forming a compound with M or M', and x, x', y, y'are of M, M', A. It represents the composition ratio of the compound determined by the valence, and the solubility product K _sp is a value in an aqueous solution at 25 ° C.
The metal compound M _x A _y is a metal compound that is easily dissolved (the solubility product K _sp is large), and the metal compound _M'x' A _y'is a metal compound that is difficult to dissolve (the solubility product K _sp is small). Is.

If the difference Δ of the solubility product is 10 or more, it is considered that the ion exchange reaction proceeds between M and M'. The larger the difference in solubility product Δ, the faster the ion exchange reaction rate, that is, the faster the formation of the barrier sheet by the ion exchange reaction, which is preferable. In particular, when the solubility product K _{sp of the metal compound M x} A _y to be extracted is very large, the dissolution rate in the electrolytic solution is very fast, but it is dissolved by accelerating the formation of the barrier sheet. It is possible to suppress the dissolution of the easy metal compound M _{x Ay} (in other words, a barrier sheet is formed before the extraction target is dissolved, and the dissolution of the extraction target can be suppressed).

In this respect, Δ is preferably 11 or more, more preferably 12 or more, further preferably 13 or more, further preferably 14 or more, more preferably 15 or more, and 16 or more. More preferably, it is more preferably 17 or more, more preferably 18 or more, further preferably 19 or more, further preferably 20 or more, more preferably 21 or more, and further preferably 22 or more. It is more preferable that it is 23 or more larger, more preferably 24 or more larger, more preferably 25 or more larger, further preferably 26 or more larger, further preferably 27 or more larger, further preferably 28 or more larger. 29 or more is more preferable, 30 or more is more preferable, 31 or more is larger, 32 or more is more preferable, 33 or more is more preferable, 34 or more is more preferable, and 35 or more is 35 or more. Larger is more preferable, 36 or more is more preferable, 37 or more is more preferable, 38 or more is more preferable, 39 or more is more preferable, and 40 or more is more preferable.

Table 1 shows the difference Δ _{between the solubility product K sp} of the sulfide at 25 ° C. in the aqueous solution and the pK _sp (= −log ₁₀ K _{sp) between the sulfides.} In the table, the double-line frame (or dark gray frame) is _{a combination of sulfides having a pK sp} difference Δ of 22 or more, and these combinations facilitate the ion exchange reaction and the resulting barrier sheet formation. Or it is expected to progress in seconds. Expressed simply with a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as ◎. The thick line frame (or light gray frame) is _{a combination of sulfides with a pK sp} difference Δ of 10 or more and less than 22, which may take minutes to hours, but the ion exchange reaction and the resulting barrier. Sheet formation is expected to progress. Expressed simply as a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as ○ to △. The thin line frame (or white frame) is _{a combination of sulfides having a pK sp} difference Δ of less than 10, and it is expected that the ion exchange reaction and the resulting barrier sheet formation will not proceed easily with these combinations. Expressed simply as a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as Δ to ×.
Regarding the solubility product of sulfides, some sulfides of the same element show different solubility products depending on the crystal morphology and the like. Table 1 lists sulfides having a crystal morphology or the like in which the difference Δ of _{pK sp becomes small.} This may be in the form of the difference between the pK _sp delta increases, the difference between the pK _sp of the sulfide to be delta becomes 10 or more, it is considered that exchange reaction proceeds.

Further, in Table 1, the _{sulfide having the largest solubility product K sp} is MnS, but in reality, there are compounds such as MgS that are more soluble than MnS. However, the solubility of MgS and the like is very large, and there is no accurate measured value. However, empirically, the presence of easily soluble compounds than MnS as MgS is known, the solubility product K _sp is considered to be greater than the solubility product K _sp of MnS. Therefore, Δ when the compound more soluble than MnS such as MgS is the extraction target compound M _{x Ay} can be regarded as larger than Δ when the extraction target compound is MnS.

The extraction target M _{x Ay} may be a metal compound having a solubility product K _sp larger than MnS, that is, a metal compound having a solubility product K _sp larger than 3 × 10 ^-14. Therefore, the extraction target M _x A _y may be MgS.
A metal compound having such a large solubility product K _sp (for example, MgS) easily dissolves in a normal electrolytic solution, but the present invention suppresses the dissolution and has the effect of obtaining data that could not be obtained accurately so far. Can be remarkably enjoyed.

The above solubility product K _sp is a value in an aqueous solution, but it is presumed that the same tendency is observed in a non-aqueous solvent such as methanol, which is the same polar solvent. From this, the electrolytic solution of the present invention may be a non-aqueous solvent system.

The present inventors conducted tests, and as shown in Table 2, the difference Δ of _{pK sp} (-log ₁₀ K _sp ) obtained from _{K sp was 10 or more even when a non-aqueous solvent (lower alcohol) was used.} It has been confirmed that a reaction is observed. Specifically, the following confirmation test was conducted.
-Two types of steel materials containing MgS (those with a diameter of MgS of 1 μm or more and those with a diameter of 100 to 150 nm) were prepared as samples containing the extraction target, and their surfaces were mirror-polished. ..
-As metal M'+ ions for ion exchange, 6 types of standard solutions (M'+ solution) for atomic absorption spectrometry having a metal ion concentration of Ag, Cu, Pb, Co, Zn, and Ni of 1000 μg / ml, respectively. I prepared it. 0.1 ml of M'solution was mixed with 0.3 ml of methanol as a non-aqueous solvent.
-A mixed solution was applied to the surface of the steel material, and changes in the surface of the steel material were confirmed.
In the case where the mixed solution containing Ag and Cu was applied, the surface of the steel material turned black within 5 minutes from the application. In the case where the mixed solution containing Pb was applied, the surface of the steel material turned black in about 10 minutes from the application. In the case where the mixed solution containing Co, Zn and Ni was applied, the surface of the steel material turned black in about 20 minutes after the application.
-Furthermore, when SEM and EDS observations were performed on the discolored steel material, it was confirmed that ion exchange between Mg and metal M'(that is, barrier code formation) occurred on the surface of the MgS particles. ..
From this, in the scope of the present invention, the solubility product K _sp is an index in an aqueous solution, but it can be applied to a non-aqueous solution, and the solubility product K _sp there shows the same tendency as in an aqueous solution. Is estimated.
-It was also confirmed that the larger the difference Δ of _{pK sp, the faster the ion exchange reaction.} On the other hand, it was also confirmed that the ion exchange reaction proceeded steadily, although the reaction rate was relatively slow even if the difference Δ of _{pK sp was small.}

The reaction on the surface of the metal compound to be extracted will be described. Here, an example is used in which the metal compound to be extracted is MgS and the metal ion to be ion-exchanged is Ag ion. First, sulfides Ag, since the difference between the _{pK sp} of MnS delta is 36.6, the difference delta is larger the _{pK sp} with MgS, readily produce Mg ion exchange reaction MgS particle surface.
Ag ions are Mg and ion exchange surface of MgS particles, the expelling Mg ions in the electrolyte solution, itself, remains as Ag ₂ S in MgS particle surface. _{Ag 2} S formed on the surface has low solubility and acts as a barrier sheet that suppresses the dissolution of MgS particles coated on the surface layer.

The general reaction mechanism is as follows.

MgS + Ag ion → Ag ₂ S + MgS (covered by Ag) Does not decompose into water.

Further, when the electrolytic extraction time is prolonged, the surface of MgS particles coated with a barrier sheet of Ag 2 _S, sometimes progresses further ion exchange reaction. That is, it toward the inside from the surface of MgS particles, it will be infiltrated with Ag 2 _S. The central portion of the MgS particles may be completely ion-exchanged with Ag.

Further, Ag ₂ S is easily reduced when it reacts with H ions and can exist as a metal Ag, and the metal Ag is insoluble in water. In general, since H ions are also contained in the electrolytic solution, at least a part of the surface of MgS particles may be coated with a barrier sheet made of metal Ag.

Thus, hitherto the MgS particles had gotten dissolved in the electrolytic solution, Ag 2 by _S or Ag can be coated with a barrier sheet, be present stably in the precipitates and inclusions This makes it possible and can be useful for estimating the size distribution of MgS particles, the number density, and the like.
To the center portion of the MgS particles even completely infiltrated with Ag, through observation of the infiltrated Ag 2 formed _S particles or even reduced the Ag particles and the size distribution of MgS particles that were present in the steel, It can be useful for estimating the number density and the like.

As the metal M'for forming the barrier sheet that causes the ion exchange reaction, _{it is considered that the larger the pK sp} difference Δ with respect to the _{metal compound M x} A _y to be extracted, the easier it is to form the barrier sheet, which is preferable. In this respect, greater _pK metal compound having a _sp M _{'x' 'metal} M' A _y is, Hg, Ag, Cu, Pb , Cd, Co, may be at least one of Zn, and Ni, these become the metal M 'ions, it can be a barrier sheet of metal compound _M x _{a y} with small _{pK sp.}

Metal M ', and as a method to be added to the electrolytic solution, the metal M' compounds, such as _'may be added in the form of a metal M' M _'x' A y be added in the form of a solution containing ions It may be added well or in the form of metal M'and then dissolved in the electrolytic solution.

Since the metal M'may be contained in the steel sample, it is preferable to add a metal not contained in the steel sample to the electrolytic solution. This is because the difference between what is contained in the steel sample and what is added to the electrolytic solution is clear, and the subsequent analysis is clear. In this respect, Hg and Ag generally have a low content in steel, and are therefore suitable as the metal M'added to the electrolytic solution. Further, the compounds of Hg and Ag are also suitable in that the solubility product is small, that is, the ability to form a barrier sheet is considered to be high. Therefore, the metal M'may be at least one of Hg and Ag.

The electrolytic solution according to the present invention may have a metal M'concentration of 0.0002 to 0.2% by mass. If the metal M 'is 0.0002 wt% (2 ppm) or more, sufficient, it is the extraction target (easy dissolution) to form a barrier sheet on the surface of the compound _M x _{A y.} It is possible to further increase the metal M'concentration in the electrolytic solution, and it may be appropriately adjusted according to the amount of the extraction target. However, even if the metal M'concentration is increased, the ion exchange rate is not improved and the cost is only increased. Therefore, the upper limit of the concentration may be 0.2% by mass (2000 ppm).

A in the metal compounds M _x A _y , _M'x' A _y'is a monatomic or atomic group forming a compound with M or M', and is an atom of C, N, H, S, O, P and F. It may contain one or more atoms independently selected from the group consisting of.

The electrolytic solution may be agitated in the electrolytic cell. As a result, _{the surface of the compound M x Ay} to be extracted is likely to come into contact with the metal M'ions, and a barrier sheet is easily formed. The means of stirring is not particularly limited, but bubbling by a bubble generator, vortex flow by a magnetic stirrer, or the like may be used. Alternatively, droplets of the solution containing metal M'ions may be dropped in the vicinity of the steel material containing the extraction target. The lower limit may be 100 cc / min, preferably 200 cc / min for bubbling, and 100 rpm, preferably 200 rpm for stirrers, so that they can easily come into contact with metal M'ions. When bubbling amount and stirrer speed is too high, delamination and the electrolytic object surface, dissolution of the compound M _x A _y is the extraction target results in a problem that is facilitated. Therefore, the upper limit may be 600 cc / min for bubbling, preferably 500 cc / min, and 600 rpm for a stirrer, preferably 500 rpm.
When stirring the electrolytic solution in a general electrolytic operation, the stirring operation is performed so that the flow of the electrolytic solution generated by the stirring does not come into contact with the object to be electrolyzed. This is based on the idea that the flow of the electrolytic solution generated by stirring does not affect the object to be electrolyzed. In the present invention, the metal M 'ion forming the barrier sheet is, in terms of easy contact with the surface of a extraction target compound M _x A _y, so that the electrolyte flow caused by stirring or the like in contact with the electrolyte object May be agitated or supplied.
Examples of the gas for bubbling include nitrogen gas and an inert gas such as helium and argon. An active gas such as oxygen or hydrogen is not preferable because it may affect the dissolved oxygen concentration in the electrolytic solution and may affect the object to be electrolyzed.

The metal material in the present invention may be a steel material. The steel material refers to a material containing iron as a main component and may contain a trace amount of carbon.

When the electrolytic solution after etching is passed through a filter and the metal compound particles are extracted as the collected residue, the filter may be a tetrafluorinated ethylene resin filter. A conventionally used nucleo-pore filter is used as a filter for filtering inclusions, precipitation phase 5 and residue 11 from an electrolytic solution in order to identify and quantitatively analyze inclusions, precipitation phase 5 and residue 11 (not shown). In (manufactured by GE), it is difficult to filter out the residue due to dissolution damage.

INDUSTRIAL APPLICABILITY The present invention may also provide analysis of metal compound particles extracted by the above method. The metal compound particles may be subjected to a schematic composition analysis by XRF or a precise composition analysis by ICP. Further, as the surface analysis method, observation by SEM, elemental analysis by EDS, or the like may be used. By analyzing the surface of the sample from which the metal compound is extracted during the etching, it is possible to observe the situation where the metal compound is extracted in chronological order.

According to the present invention, it is possible to suppress the dissolution of precipitates and inclusions which are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol in an electrolytic solution, and as a result. , An electrolytic solution capable of obtaining accurate data on their precipitates, size distribution of inclusions, number density, and an electrolytic extraction method can be provided.

In the above description, a metal sulfide is mainly used as the metal compound, but the metal compound is not limited to the sulfide. It is considered that the formation of a barrier sheet can occur depending on the difference in solubility product of any of the compound species. Table 3 shows the difference Δ _{of pK sp} (= −log ₁₀ K _sp ) between the selenium compounds at 25 ° C. in the aqueous solution. In Table 3, the double-line frame (or dark gray frame) is _{a combination of serene products having a pK sp} difference Δ of 22 or more, and these combinations facilitate the ion exchange reaction and the formation of a barrier sheet by the combination. Expected to progress in or in seconds. Expressed simply with a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as ◎. The thick line frame (or light gray frame) is _{a combination of serene products with a pK sp} difference Δ of 10 or more and less than 22, which may take several minutes to several hours, but the ion exchange reaction and the resulting barrier. Sheet formation is expected to progress. Expressed simply as a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as ○ to △. The thin line frame (or white frame) is _{a combination of selenium compounds having a pK sp} difference Δ of less than 10, and it is expected that the exchange reaction and the resulting barrier sheet formation will not proceed easily with these combinations. Expressed simply as a symbol, the degree of expectation (prediction) of the exchange reaction is expressed as Δ to ×.

According to the present invention, it can also be applied to selenium products.

Further, according to the present invention, the metal compound particles are extracted by using the above-mentioned electrolytic solution in a form in which at least the surface of the particles of the _{metal compound M x} A _{y to be extracted is coated with the metal M'or the compound.} Extraction methods are also provided.

The electrolytic solution according to the present invention may contain a particle dispersant such as SDS as a component other than the above.

Hereinafter, the present invention will be described through examples. However, the invention of the present application should not be construed as being limited to the following examples.

The inclusions or the precipitated phase in the steel sample were observed by the electrolytic solution and the electrolytic method according to the present invention.
As a steel sample, C: 0.07 wt%, Si: 0.05 wt%, Mn: 1.45 wt%, S: 0.005 wt%, Cu: 0.3 wt%, Al: 0.08 wt%, Mg: 0. A steel material for thick plates containing 007 wt% was processed into a size of 20 mm × 40 mm × 2 mm and mirror-polished. The obtained steel material was subjected to electrolytic etching by constant current electrolysis with the apparatus shown in FIG. 1 for about 20 coulombs.
The following two types of electrolytic solutions were used to observe inclusions or precipitated phases of the same steel sample.
(1) Electrolyte of Comparative Example: Electrolyte (4) containing 4% by mass methyl salicylate + 1% by mass salicylic acid + 1% by mass tetramethylammonium chloride (TMC) capable of recovering conventionally known sulfide-based inclusions as a residue. % MS)
(2) Electrolyte according to the present invention: 1 ml of a 1000 ppmAg standard solution for atomic absorption (5% HNO3) was added to 500 ml of the above 4% MS electrolyte solution to obtain a concentration equivalent to 2 ppmAg.
The solvent used was methanol in both (1) and (2).
After the completion of the electrolytic etching, the electrolytic solution was further immersed in each electrolytic solution for about 40 minutes and left to stand, and then the electrolytic solution was dropped with clean methanol, and then the steel sample was air-dried and subjected to SEM observation.

SEM-EDS Analysis Results EDX analysis of fine particles on the surface of the steel sample obtained by etching with the electrolytic solution of Comparative Example (1) and Example (2) of the present invention was performed.
In Comparative Example (1), a peak of MnS was observed, but a peak of Mg was not observed. This is because MgS was easily dissolved in the electrolytic solution.
In Example (2) of the present invention, unlike Comparative Example (1), a peak of Mg and a peak of Ag coated on the surface layer of fine particles appeared. This water, Ag ions easily soluble MgS surface in methanol or the like to attack by causing an ion exchange reaction (Mn, Mg) in the surface layer of S particles, insoluble in water is high, Ag 2 S _or, It can be understood that because the Ag coating was formed, it did not dissolve even after being left in the electrolytic solution for 40 minutes.

FIG. 2 shows an SEM-EDS image of fine particles on the surface of a steel sample obtained by etching with the electrolytic solution of (2). In FIG. 2, the upper left image is an SEM observation image of the observed fine particles, the upper right image shows the SEM observation image overlaid with the Ag concentration chart measured by EDS, and the lower left image shows the Mg concentration chart. It is shown in an overlapping manner, and the lower right image shows the S density chart in an overlapping manner.
From the chart of the element concentration in FIG. 2, it is confirmed that the surface portion of the MgS particles is replaced with Ag 2 _S or Ag. Although the height (concentration) of each element in the chart is relative, the following can be read. Specifically, spherical fine particles having a diameter of about 100 nm can be confirmed, and the values of the graphs of Ag, Mg and S rise in a chevron shape in the range where these fine particles exist, and the fine particles are centered (MgS). ) has a nucleus, its circumference was coated with Ag ₂ S or Ag. A schematic cross-sectional view of the fine particles created based on this finding is as shown in FIG. Were electrolytically extracted by the present invention, the particle size of the Ag 2 _S or Ag in the barrier coat was MgS particles on the surface was confirmed mirror polished surface of the steel sample before electrolysis was observed by SEM-EDS MgS It was almost the same as the particle size of.

From the above results, when a steel sample was electrolyzed using a conventional electrolytic solution, and observation by SEM or the like and micro analysis by EDS were performed, MgS originally observed in the steel material was dissolved in the electrolytic solution. Was confirmed.
On the other hand, when the electrolytic solution according to the present invention is used, the MgS is coated with Ag without causing the above-mentioned problems, so that dissolution is suppressed and the MgS particles can be stably contained in the electrolytic solution. I was able to make it exist. As a result, easily soluble metal compounds such as MgS, which have been dissolved and could not be analyzed, can be observed by SEM and micro-analyzed by EDS, which greatly contributes to the improvement of analysis accuracy of steel samples. Can be done.

By electrolyzing a steel sample using the electrolytic solution according to the present invention, precipitates and inclusions that are stable in steel but easily hydrolyzed in an aqueous solution or an organic solvent such as ethanol or methanol are contained in the electrolytic solution. It is possible to provide an electrolytic solution capable of suppressing dissolution in a solvent, and as a result, an electrolytic solution capable of obtaining accurate data on their precipitates, size distribution of inclusions, and number density, and an electrolytic extraction method.

4 Metal sample 5 Inclusions / precipitated phase grains 6 Electrode (cathode side)
7 Reference electrode 8 Power supply (potentiometer)
9 Electrolyte 10 Electrolytic cell

Claims (8)

An electrolytic solution used when etching a metal material and extracting metal compound particles in the metal material.
The solubility product of the _{metal compound M x} A _{y to} be extracted contained in the metal material _{is K sp} [M _x A _y ].
When _'the solubility product _{K sp} [M' metal compound M _'x' A _y and _{x 'A y'],}
An electrolytic solution characterized by containing ions of a metal M'defining by the following formula and having a Δ of 10 or more.
_{Δ = pK sp [M 'x} ' A y '] -pK sp [M x A y]
_{= (- log 10 K sp [} M 'x' A y ']) - (- log 10 K sp [M x A y])
Here, M and M'are different metal elements, A is a single atom or atomic group forming a compound with M or M', and x, x', y, y'are of M, M', A. It represents the composition ratio of the compound determined by the valence, and the solubility product K _sp is a value in an aqueous solution at 25 ° C. The electrolytic solution according to claim 1, which is a non-aqueous solvent system. The electrolytic solution according to claim 1 or 2, wherein the metal compound M _x A _{y to be extracted is MgS.} The electrolytic solution according to any one of claims 1 to 3, wherein the metal M'is at least one of Hg, Ag, Cu, Pb, Cd, Co, Zn, and Ni. The electrolytic solution according to any one of claims 1 to 4, wherein the concentration of the metal M'is 0.0002 to 0.2% by mass. The electrolytic solution according to any one of claims 1 to 5, wherein the metal material is a steel material. The electrolytic solution according to any one of claims 2 to 5, wherein the non-aqueous solvent contains at least one of methanol and ethanol.
In a method of etching a metal material in an electrolytic solution and extracting metal compound particles in the metal material,
Using the electrolytic solution according to any one of claims 1 to 7, _{the particles of the metal compound M x} A _y to be extracted are electrolytically extracted in a form in which at least the surface is coated with the metal M'or the compound. A method for extracting metal compound particles.

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